1. Field of the Invention
The present invention generally relates to high sensitivity magnetic field detection, more specifically to high sensitivity magnetic field detection without superconducting quantum interference devices (SQUIDs), and still more specifically to room temperature NMR/MRI and direct magnetic field detection through the application of a laser based atomic magnetometer.
2. Description of the Relevant Art
High sensitivity detection of magnetic fields has previously been possible only with superconducting quantum interference devices (SQUIDs), or with Faraday detection coupled with an extremely high measurement field.
U.S. Pat. No. 7,061,237, issued Jun. 13, 2006 to Pines et al, incorporated by reference in its entirety, relates to an apparatus and method for remote NMR/MRI spectroscopy having an encoding coil with a sample chamber, a supply of signal carriers, preferably hyperpolarized xenon and a detector allowing the spatial and temporal separation of signal preparation and signal detection steps. This separation allows the physical conditions and methods of the encoding and detection steps to be optimized independently. The encoding of the carrier molecules may take place in a high or a low magnetic field and conventional NMR pulse sequences can be split between encoding and detection steps. In one embodiment, the detector is a high magnetic field NMR apparatus. In another embodiment, the detector is a superconducting quantum interference device. A further embodiment uses optical detection of Rb—Xe spin exchange. Another embodiment uses an optical magnetometer using non-linear Faraday rotation. Concentration of the signal carriers in the detector can greatly improve the signal to noise ratio. Remote detection is a hallmark of this invention.
U.S. Pat. No. 7,053,610, issued May 30, 2006 to Clarke et al., incorporated by reference in its entirety, relates to SQUID detected NMR and MRI at ultralow fields. Here, nuclear magnetic resonance (NMR) signals are detected in microtesla fields. Prepolarization in millitesla fields is followed by detection with an untuned dc superconducting quantum interference device (SQUID) magnetometer. Because the sensitivity of the SQUID is frequency independent, both signal-to-noise ratio (SNR) and spectral resolution are enhanced by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. MRI in ultralow magnetic field is based on the NMR at ultralow fields. Gradient magnetic fields are applied, and images are constructed from the detected NMR signals.
Detractions of the Clarke et al. patent are that cryogenic temperatures are required, as well as cumbersome thermal shielding between the cryogenic SQUID and the room temperature sample or subject. A great improvement of the technology would be available if low field NMR and MRI could be obtained without the cumbersome cryogenic requirements. An even greater improvement would be if the measurement fields were irrelevant, and completely unnecessary.